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Na + channel inactivation: a comparative study between pancreatic islet β‐cells and adrenal chromaffin cells in rat
Author(s) -
Lou XueLin,
Yu Xiao,
Chen XiaoKe,
Duan KaiLai,
He LiMing,
Qu AnLian,
Xu Tao,
Zhou Zhuan
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j..2003.t01-1-00191.x
Subject(s) - hyperpolarization (physics) , membrane potential , endocrinology , chromaffin cell , enteroendocrine cell , medicine , chemistry , patch clamp , beta (programming language) , biophysics , electrophysiology , biology , microbiology and biotechnology , adrenal medulla , endocrine system , hormone , catecholamine , organic chemistry , nuclear magnetic resonance spectroscopy , computer science , programming language
A comparative study was carried out on the inactivation of Na + channels in two types of endocrine cells in rats, β‐cells and adrenal chromaffin cells (ACCs), using patch‐clamp techniques. The β‐cells were very sensitive to hyperpolarization; the Na + currents increased ninefold when the holding potential was shifted from −70 mV to −120 mV. ACCs were not sensitive to hyperpolarization. The half‐inactivation voltages were −90 mV (rat β‐cells) and −62 mV (ACCs). The time constant for recovery from inactivation at −70 mV was 10.5 times slower in β‐cells (60 ms) than in ACCs (5.7 ms). The rate of Na + ‐channel inactivation at physiological resting potential was more than three times slower in β‐cells than in ACCs. Na + influx through Na + channels had no effect on the secretory machinery in rat β‐cells. However, these ‘silent Na + channels’ could contribute to the generation of action potentials in some conditions, such as when the cell is hyperpolarized. It is concluded that the fractional availability of Na + channels in β‐cells at a holding potential of −70 mV is about 15 % of that in ACCs. This value in rat β‐cells is larger than that observed in mouse (0 %), but is smaller than those observed in human or dog (90 %).